The prior art discloses a number of construction machines having either four points of suspension for a flexible frame on four endless tracks, one at each corner; or three points of suspension on a pair of endless tracks, one on each side of the machine having a rigid frame. Notable among these are the machines disclosed in EARLY U.S. Pat. No. 2,844,882; GUNTERT U.S. Pat. No. 2,864,452; KNOX U.S. Pat. No. 2,202,009; STEVENS U.S. Pat. No. 2,128,273 and ALLEN U.S. Pat. No. 2,128,889 along with CURLETT et al U.S. Pat. No. 3,230,846; CURLETT U.S. Pat. No. 3,249,026; SWISHER et al U.S. Pat No. 3,423,859 and SNOW et al U.S. Pat. No. 3,540,360. The two track machines steer by crabbing, a function which causes the machine to steer in an uneven wobbly path that has a serious effect on the control of the grade, slope and direction of the tool. The machine of MILLER et al U.S. Pat. No. 3,606,827 (by the instant inventors) overcomes this and other defects by using four tracks, one at each corner, two of which on one side carry the rigid frame at a pivot point central of a walking beam. The opposite front pair and the opposite rear pair of tracks are tied together by linkages so that as to be steerable in pairs, i.e., like the front wheels of an automobile. SWISHER et al provide a similar steering arrangement operating from a guide line on each side of the machine. The SWISHER et al machine has a flexible frame and can be raised to position the frame over a truck and the track support members are pivoted upwardly off the ground for movement by the truck to a new location. For longer hauls, the four track support members are removed and transported on a separate truck.
Road construction machines, such as that disclosed in SWISHER et al U.S. Pat. No. 3,423,859 are designed to span the width of one or more lanes of a highway for which purpose sizeable flexible frames and/or elongated track support beams are required. Understandably some provisions must be made for reducing the overall size of the machine for transport from one work location to the other, even to the extent of actually disconnecting the tracks from the frame. Finite adjustment of slope and grade are best provided in machines having a rigid frame.